Photochromic materials are generally capable of converting from a first state, for example a “bleached state,” to a second state, for example a “darkened state,” in response to exposure to actinic radiation, and reverting back to the first state when exposure to the actinic radiation is discontinued or reduced. Thus, photochromic materials are used in photochromic articles, such as optical articles, to provide a reversible change in color when exposed to actinic radiation that includes ultraviolet (UV) light. Examples of such optical articles are sunglasses, vision correcting ophthalmic lenses, non-prescription and prescription lenses, sport masks, face shields, goggles, visors camera lenses, windows, and automotive windshields.
A combination of photochromic materials can be incorporated into a single layer of a photochromic article for purposes such as obtaining a desired color when activated. The photochromic performance, e.g., optical density and/or fade half-life, of such photochromic articles can, however, be less than optimal.
It would be desirable to develop new photochromic articles that include a combination of photochromic compounds, which provide improved photochromic performance.